1. Field of the invention:
The present invention relates to a zoom lens mount assembly for use in optical apparatus such as photographic camera, handy motion picture camera, video camera, copying machine or enlarger.
2. Background art:
The zoom lens mount assembly of well known art for use in the optical apparatus such as the photographic camera or the video camera principally comprises the cam sleeve having the elongate cam tracks extending circumferentially therearound and the movable sleeve having the cam followers (i.e., the pins provided with the rollers) extending through said cam tracks and movably supported inside said cam sleeve so that the optical system carried by said movable sleeve can be magnification-varied as said movable sleeve is moved in parallel to the optical axis by rotationally driving said cam sleeve.
In practice, a plurality of said movable sleeves are provided inside the cam sleeve so that the respective movable sleeves are guided by the stationary sleeve and moved in operative association with the cam sleeve.
The zoom lens mount assembly of this type is, however, disadvantageous in that the outer diameter of the lens mount assembly will become inconveniently large when it is desired to obtain a given inner diameter thereof and the inner diameter of the lens mount assembly will be unacceptably reduced when it is desired to limit the outer diameter thereof, because this zoom lens mount assembly is of a multi-layered cylindrical construction.
Additionally, in view of the fact that said cam tracks of the cam sleeve are defined by elongate slots extending circumferentially therearound, it is difficult to obtain this cam sleeve by molding of synthetic resin material and, in consequence, the cam sleeve has usually been made of metallic material. This inevitably reduces the efficiency of production and increases the cost of parts.
However, the cam sleeve molded from synthetic resin material is known, for example, from U.S. Pat. No. 3,744,884.
According to this U.S. Patent, the cam surface portion 20 of the first barrel portion 16 forms in cooperation with the cam surface portion 40 of the second barrel portion 24 the first cam track 44 along which the cam stud 54 of the lens carrier body 50 is moved. The width of the cam track is given by the spacer members 36. Similarly, the cam surface portion 60 of the first barrel portion 16 forms in cooperation with the cam surface portion 66 of the third barrel portion 62 the second cam track along which the cam stud 80 of the lens cell 76 is moved.
Displacement of the lens is achieved by moving the sleeve 90 by operation of the control handle 100.
The arrangement disclosed by this U.S. Patent is inconvenient in that the number of parts is relatively many since the cam barrel comprises three barrel portions (16, 24, 62) and, in addition, a desired high precision of the cam cannot be expected because these three barrel portions (16, 24, 62) are secured together by use of screws.
Furthermore, the first, second and third barrel portions include their respective cam surface portions defined by the notches and, therefore, these barrel portions are necessarily deformed during a post-shrinkage process of molding. This deteriorates the true circularity of the respective barrel portions and also reduces the cam precision.